Holding system, exposure apparatus, and device manufacturing method

ABSTRACT

Disclosed is a holding system for holding an object from the above, against gravity, and it includes at least one holding portion adapted to be in contact with the object, to hold the object from the above, and at least one attracting portion for attracting a limited portion of the object upwardly, without contact thereto.

This application is a divisional application of copending U.S. patentapplication Ser. No. 10/987,148, filed Nov. 15, 2004.

FIELD OF THE INVENTION

This invention relates generally to a holding technique for holding anobject and, more particularly, to a holding system usable in an exposureapparatus for a lithographic process in the manufacture of circuitdevices, such as semiconductor devices or liquid crystal displaydevices, for holding a reflecting optical element, for example.

The manufacture of semiconductor devices currently uses a step-and-scantype scanning exposure apparatus in which ultraviolet pulse laser lighthaving a wavelength of 248 nm from a KrF excimer laser light source oran ultraviolet pulse laser light having a wavelength of 193 nm from anArF excimer laser light source is used as illumination light, andwherein a mask or reticle (hereinafter, simply “reticle”) having acircuit pattern formed thereon and a wafer (photosensitive substrate)are one-dimensionally scanningly moved relative to the projection filedof a reduction projection optical system, whereby the circuit pattern asa whole is transferred to a single shot region on the wafer. Such a scanexposure operation is followed by stepwise motion, and these operationsare repeated.

It is certain that the density of a semiconductor device is in thefuture raised more and more, and the device rule would not be greaterthan 0.1 ìm, that is, 100 nm L/S (line-and-space). There are manytechnical problems to be solved, to meet this requirement by use of anexposure apparatus in which ultraviolet pulse laser light having awavelength of 193 nm is used as illumination light.

In recent years, extreme ultraviolet (EUV) exposure apparatuses usinglight in a soft X-ray region of a wavelength of 5 nm-15 nm (hereinafter,this light will be referred to as “extreme ultraviolet light” or “EUVlight” in this specification) have been developed, and they have becomeattractive as next generation exposure apparatuses or a minimumlinewidth of 100 nm.

Such an EUV exposure apparatus must be placed in a vacuum ambience, andthe optical system has to be a reflection optical system, as contrastedto conventional exposure apparatuses.

Furthermore, as regards the precision, extremely strict precision isrequired with respect to reticle-to-wafer alignment precision, waferpositioning precision, including stepping precision, distortion andfocus of the projection optical system, and so on.

As regards the reticle structure, in dependence upon the number ofmirrors of a reflection type projection optical system, it would benecessary that the mask be supported upside down. Furthermore, becauseof vacuum ambience, vacuum attraction is inappropriate, andelectrostatic attraction has to be used to hold a reticle or a wafer. Onthe other hand, in regards to the precision of the surface shape of thereticle, a strict precision of a nm level is unexceptionally appliedthereto. Additionally, correction of an error is very difficult toachieve.

When an electrostatic attraction force is used in a vacuum ambience tohold a reticle from above, with a pattern bearing surface (reflectionsurface) of the reticle held facing down, the following inconveniencesare caused: (1) if a reticle is supported at three or four points alongits periphery, self-weight flexure will be produced which, in turn, willcause defocus of a non-negligible amount; (2) as compared with aconventional transmission type reticle, a reflection type reticle can beheld by gripping the back surface thereof, but when the back surface asa whole (containing a surface-step structure) is gripped, and, if thereis a foreign particle sandwiched, it causes surface strain and defocus,as well; and (3) since the electrostatic chuck itself generates heat,due to thermal expansion of the chuck, a deviation is produced betweenthe chuck and the reticle.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide aholding technique by which at least one of the inconveniences describedabove can be solved or reduced.

It is another object of the present invention to provide a holdingtechnique by which the shape of an object to be held can be controlled.

In accordance with an aspect of the present invention, to achieve atleast one of the objects described above, there is provided a holdingsystem for holding an object from above, against gravity, the holdingsystem comprising at least one holding portion adapted to be in contactwith the object, to hold the object from above, and at least oneattracting portion for attracting a limited portion of the objectupwardly, without contact thereto.

Thus, according to the present invention, a holding technique by whichthe shape of an object to be held can be controlled, is provided.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a general structure of a reticle chuckaccording to an embodiment of the present invention.

FIG. 2 is a schematic view of a general structure of an exposureapparatus into which the reticle chuck of FIG. 1 is incorporated.

FIG. 3 is a flow chart for explaining a reticle correction sequence tobe performed with the structure of FIG. 1.

FIG. 4 is a schematic view of a general structure of a reticle chuckaccording to another embodiment of the present invention.

FIG. 5 is a flow chart for explaining the procedure of devicemanufacture.

FIG. 6 is a flow chart for explaining details of a wafer processincluded in the procedure of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one preferred embodiment of the present invention,the object to be held is supported at least at one point and,additionally, in a region other than this, at least one electrostaticchuck is provided without contact to the object. The electrostatic chuckprovided in non-contact (hereinafter, “non-contact electrostatic chuck”)is arranged to partially deform the shape of the object by itsattraction force, without contact to the object.

Another preferred embodiment of the present invention concerns asubstrate holding system for holding a substrate, wherein the substrateis supported at least one point, preferably, at three points, and, in aregion of the substrate other than this portion, at least oneelectrostatic chuck is provided without contact to the substrate. Theholding means for holding the substrate at the three points preferablycomprises one of electrostatic attracting means, vacuum attractingmeans, electromagnetic attracting means and mechanical gripping means.

In one preferred form of the present invention, the non-contactelectrostatic chuck has a function for correcting self-weight flexure ofthe substrate by its attraction force, without contact to the substrate.

In one preferred form of the present invention, the non-contactelectrostatic chuck has a function for partially deforming the shape ofthe substrate by its attraction force, without contact to the substrate.

In one preferred form of the present invention, a plurality ofnon-contact chucks are preferably provided, each being the non-contactchuck as described above.

The clearance between the non-contact chuck and the substrate maypreferably be 20 ìm or less, more preferably, not greater than 5 ìm.

The non-contact chuck may preferably have a temperature adjustingfunction.

In one preferred form of the present invention, the non-contactelectrostatic chuck is provided with gas measuring means for measuringthe gap between the chuck and a reticle.

In one preferred form of the present invention, a control system isprovided to feed back a measured value of the gas measuring means to theattraction force of the non-contact electrostatic chuck.

In a substrate holding system for holding a substrate according to onepreferred form of the present invention, height measuring means isprovided to measure the height (level) of the substrate.

In one preferred form of the present invention, the attracting force ofthe non-contact electrostatic chuck is changed in accordance with ameasured value of the height measuring means.

The substrate may be a reflection type reticle having a circuit patternformed on a glass substrate. The substrate holding at three peripheralpoints may be attained by an electrostatic chuck and, preferably, thereticle is held at its bottom face outside the pattern region on thepattern bearing surface.

In one preferred form of the present invention, a base plate to whichthe non-contact electrostatic chuck is fixed is made of a low thermalexpansion material.

Preferably, the base plate is made of the same material as that of thereflection type mask having a circuit pattern formed on a glasssubstrate.

The material of the base plate may preferably be ceramics or glass,having a linear expansion coefficient of 10⁻⁶ or less.

The base plate may preferably have temperature adjusting means providedinside thereof.

The electrostatic chuck for the three-point support may be fixed througha base plate made of the same material as that of the mask or of a lowthermal expansion material, rather than constituting it as an integralmember. On that occasion, with respect to the thermal expansion, thematerial of the electrostatic chuck need not be a particular one. Thisleads to a reduction of cost for production of the electrostatic chuck.

Another preferred embodiment of the present invention concerns a mirrorholding system for holding a mirror, wherein the mirror is supported atleast at one point, preferably, at three points, and, wherein, in aregion of the substrate other than that portion, at least oneelectrostatic chuck is provided without contact to the mirror.

Next, with reference to the attached drawings, preferred embodiments ofthe present invention will be described specifically and in detail.

Embodiment 1

A first embodiment of the present invention will be explained inconjunction with FIGS. 1-3.

FIG. 1 illustrates a general structure of a reticle chuck according to afirst embodiment of the present invention. FIG. 2 is a schematic view ofa general structure of an exposure apparatus as a whole, including thereticle chuck of FIG. 1.

The general structure of the exposure apparatus will be described first,with reference to FIG. 2.

The exposure apparatus shown in the drawings is a projection exposureapparatus which uses, as exposure light, light in a soft X-ray regionhaving a wavelength of 5 nm to 15 nm, for example, EUV exposure light 10having a wavelength of 13.4 nm or 11.5 nm, and it is arranged to performan exposure operation in accordance with a step-and-scan method. Theexposure light 10 coming along the X direction in the drawing isreflected by a mirror 11, and it is projected onto a reflection typereticle 1 having a circuit pattern formed on a glass substrate. Althoughthe reflection type reticle will be described later in detail, it isattracted and gripped by an electrostatic chuck, also to be describedlater. The reticle is placed on a reticle stage, not shown, which ismovable in the X direction in the drawing and is minutely movable withall degrees of freedom (i.e., in six axis directions).

The exposure light reflected by the reflection type reticle 1 isprojected to a reflection projection optical system. This reflectionprojection optical system comprises a first mirror 12, a second mirror13, a third mirror 14 and a fourth mirror 15. The exposure lightreflected by these mirrors is transferred to the wafer 16.

Here, the first and fourth mirrors 12 and 15 have a reflection surfaceof an aspherical surface shape. The second mirror 13 has a flatreflection surface, and the third mirror 14 has a reflection surface ofa spherical surface shape. As a matter of course, the present inventionis not limited with respect to the structure of the reflectionprojection optical system. In each reflection surface, a work precisionof about 1/50 to 1/60 of the exposure wavelength is accomplished withreference to the design value. Thus, in terms of RMS value (standarddeviation), the error will be only 0.2 nm to 0.3 nm. The material ofeach mirror is low-expansion glass or metal. On the surface of eachmirror, there is a reflection layer to EUV light that comprises amultilayered film, which may be alternately superposing two differentmaterials, as with the reflection type reticle 1.

Denoted at 17 is a wafer chuck for supporting the wafer 16, and it holdsthe wafer 16 through an electrostatic attracting force. Denoted at 18 isa wafer stage base for supporting the wafer chuck 17. The wafer stagebase is supported by a wafer stage (not shown), which is movable inhorizontal directions (X and Y directions) and also is minutely movablewith all degrees of freedom (i.e., in six axis directions).

This exposure apparatus is arranged so that an image of a portion of acircuit pattern formed on the reflection type reticle (mask) 1 isprojected onto the wafer (substrate) 16 through the reflectionprojection optical system 12-15, while, on the other hand, thereflection type reticle and the wafer 16 are relatively scanningly movedin a one-dimensional direction (the X-axis direction, in this example)relative to the projection optical system 12-15, whereby the entirety ofthe circuit pattern of the reflection type reticle 1 is transferred toeach of different shot regions on the wafer 16 in a step-and-scanmethod.

Denoted at 7 is a focus sensor for measuring the position of thereflection surface of the reflection type reticle 1 with respect to theheight direction (Z direction).

Referring back to FIG. 1, the structure around the reflection typereticle 1 will be explained. In FIG. 1, denoted at 1 is a reflectiontype reticle, and it has an electrically conductive film forelectrostatic attraction, formed on the bottom face thereof. Denoted at2 is a contact type electrostatic chuck for gripping the bottom face ofthe reflection type reticle 1 at three peripheral points, through anelectrostatic attraction force. Denoted at 5 is an electrostatic chuckbase for supporting the contact type electrostatic chuck 2. Denoted at 6is a reticle stage base for supporting the electrostatic chuck base 5.The reticle stage base is supported by a reticle stage (not shown),which is movable in the X direction (scan direction) and also isminutely movable with all degrees of freedom (i.e., in six axisdirections).

Here, the electrostatic chuck base 5 is made demountably mountable tothe reticle stage base 6. As regards the material of the electrostaticchuck base 5, preferably, it may be made of the same material as that ofthe reflection type reticle 1 or made of ceramics or glass having a lowthermal expansion coefficient (e.g., not greater than 10×10⁻⁶), so as toprevent chucking shift due to heat generation of the chuck itself orheat generation by exposure.

In this embodiment, the reticle 1 is gripped at three peripheral pointsby the contact type electrostatic chuck 5. However, the number ofgripping points is not limited to this. It may be gripped at a singlepoint.

It is seen from the drawing that reticle 1, electrostatic chuck 2,electrostatic chuck base 5 and reticle stage base 6 are disposed in thisorder along the counter-gravity direction.

Denoted at 3 is a non-contact type electrostatic chuck supported by theelectrostatic chuck base 5. The non-contact type electrostatic chuck isarranged to be kept out of contact from the bottom face of thereflection type reticle 1, with a certain clearance maintainedtherebetween, when the reflection type reticle 1 is being gripped by thecontact type electrostatic chuck 2. In a portion of the reflection typereticle 1, to be opposed to the non-contact type electrostatic chuck 3,there is an electrically conductive film formed. The non-contactclearance described above may preferably be not greater than 20 ìm inthe state in which a desired flat reticle surface shape is accomplished.A clearance not greater than 10 ìm is much better. Both of the contacttype electrostatic chuck 2 and the non-contact type electrostatic chuck3 are provided with a temperature adjusting flowpassage 4 such that theycan be temperature adjusted and controlled against the heat generationin the electrostatic chuck. The surface of the contact portions(depicted by hatching in FIG. 1) of the contact type electrostatic chuck2 may be formed into a pin chuck structure of a ring chuck structure,wherein the surface is partially engraved.

In order to hold in practice the reflection type reticle 1 with thestructure described above, the reticle 1 is conveyed by a reticleconveying system (not shown) and then it is electrostatically attractedand held by the contact type electrostatic chuck 2. In this state, thereticle 1 is supported by a three-point support, and flexure by its selfweight is produced therein. Although it depends on the shape orsupporting position, according to calculations, self-weight flexure ofhundreds of nm may be caused by the three-point support. Since theexposure is made by use of a ring-like zone of exposure light, a smallflexure around the Y axis may be corrected to some degree by the reticlestage (not shown). As regards flexure around the X-axis direction,however, since it leads to defocus at the long-span side of the ring, itcannot be corrected by the reticle stage 6.

In accordance with this embodiment, in consideration of it, thenon-contact electrostatic chuck 3, being kept out of contact from thereflection type reticle 1, is arranged to produce an attracting force bywhich the reflection type reticle 1 is partially lifted upwardly tothereby correct flexure by the weight thereof. Of course, other thancorrection of the self-weight flexure, this structure may be used tointentionally cause deformation of the reflection type reticle tocorrect the shape precision of the reticle 1 or to cancel any strain ofthe optical system, for example. Because of the property of theelectrostatic chuck, if the clearance is too large, no attracting forcewill be produced. If the clearance is not greater than several tens ofmicrons, it is sufficiently possible to produce flexure of a glasssubstrate by a few microns, although the attracting force is slightlylow as compared with direct contact. Furthermore, the non-contactelectrostatic chuck is arranged to provide a variable attracting force.

Referring now to FIG. 3, showing the reticle correction sequence, thesequence up to gripping a reflection type reticle in an actual exposureapparatus will be explained.

First, a reflection type reticle 1 is attracted and gripped with thecontact type electrostatic chuck 2. The amount of idealistic self-weightflexure in this state has been detected beforehand, in accordance withcalculation or experiments. Then, the non-contact electrostatic chuck isoperated to produce, as an initial value, an attracting force effectiveto cancel the self-weight flexure of the reticle. By producing anattracting force of this initial value, a largest flexure can be almostcancelled. Subsequently, the reticle stage 6 is scanningly moved in theX direction, and the height (level) of the reflection surface of thereticle 1 is measured by use of the focus sensor 7. At this stage, anyresidual error after the self-weight flexure is cancelled or a shapeerror of the reflection type reticle 1, for example, can be measured.Furthermore, if there is any foreign particle nipped at the contact typeelectrostatic chuck, contact-gripping the reticle, it can be detected bythis measurement (it may be detected on the basis of leakage current ofthe contact type electrostatic chuck). If the presence of any particleis detected, the reticle may be collected to remove the particle or,alternatively, the influence of the particle may be cancelled bycorrection, the procedure being chosen in dependence upon the magnitudeor quantity of the particle.

If no particle is detected or, although a particle is detected, it isconcluded that it should be cancelled by correction, and respectivecorrection amounts are calculated on the basis of the result ofmeasurement described above. Here, a calculation may include correctionof strain of the optical system, as well, for example. Subsequently, onthe basis of the calculation, the applied voltage to the non-contactelectrostatic chuck 3 is changed to correct the attracting force.

Finally, as regards the component to be corrected by the reticle stage6, a corresponding signal is fed forward to a drive command for exposurescan, whereby correction is completed. The error to be corrected by thereticle stage may be mainly an error concerning average height or awedge component.

Although, in this embodiment, the reflection type reticle 1 is grippedby contact through the contact type electrostatic chuck 2, the grippingmethod is not limited to this. For example, mechanical gripping orelectromagnetic attraction gripping may be used, with similaradvantageous effects. Furthermore, although, in this embodiment, thebottom face of the reflection type reticle 1 is gripped at threeperipheral points by an electrostatic attraction force, the positions ofthese three points should preferably be at the bottom face, outside thereticle pattern region on the pattern bearing surface of the reticle. Ofcourse, the support other than the three-peripheral-point support may beused, although the effect may be slightly lower.

Embodiment 2

Referring now to FIG. 4, an exposure apparatus and an exposure methodaccording to a second embodiment of the present invention will bedescribed. In this embodiment, a contact type electrostatic chuck 2 isdisposed around a reflection type reticle 1. Also, in order to meetcorrection of any possible shape, a plurality of (more than in the firstembodiment) non-contact type electrostatic chucks are disposed. Forcorrection with better precision, the number should be larger. Denotedat 8 is a reticle gap measuring means for measuring a gap between thebottom face of the reflection type reticle 1 and the non-contactelectrostatic chuck 3. In this embodiment, for better-precision reticlecorrection, the gap between them is measured and the measured value isfed back to the attracting force, namely, the applied voltage.

Furthermore, in this embodiment, since plural electrostatic chucks areused, in order to avoid the complexity of constructing a temperatureadjustment flowpassage, a temperature adjusting flowpassage is providedin the electrostatic chuck base 5. Since the temperature of theelectrostatic chuck base 5 is controlled with this structure, heatgeneration in the individual electrostatic chucks 2 and 3 does notproduce reticle shift due to thermal expansion. The sequence up togripping a reflection type reticle in an actual exposure apparatus isapproximately the same as that of the first embodiment, and a duplicatedescription will be omitted here.

With the structure described above, correction can be done with aprecision even higher than that of the first embodiment.

The foregoing description has been mode with reference to an examplewherein a reticle is chosen as the subject of shape correction. However,as long as the correction of deformation is based on a non-contactelectrostatic attraction force, the subject is not limited to this. Forexample, substantially the same advantageous effects are obtainable whenthe invention is applied to the shape correction of a wafer or a mirror.Particularly, since the shape error of a reflection mirror used in anexposure apparatus must be controlled at a nm order, the invention iswell useful for correction of the mirror surface shape, regardless thatit is flat, spherical or aspherical.

In accordance with the embodiments of the present invention describedhereinbefore, a reflection type reticle is supported at three points,and, therefore, any distortion of the reflection surface due to anyforeign particles adhered to the reticle bottom face can be avoided.Additionally, any self-weight flexure resulting from the three-pointsupport can be corrected by means of a non-contact electrostatic chuckor chucks, and, therefore, a defocus amount in an exposure operation canbe reduced significantly. Thus, the exposure precision is improvedconsiderably.

Furthermore, the electrostatic chuck that supports the reticle at threepoints is not an integral part, but, rather, it is fixed to a stage basethrough a plate member (chuck base) 5 made of the same material as thatof the mask or of a low thermal expansion material. Therefore, withrespect to thermal expansion, the material of the electrostatic chuckneed not be a particular one. This leads to a reduction of cost for theproduction of the electrostatic chuck.

Embodiment 3

Next, an embodiment of a device manufacturing method, which uses anexposure apparatus described above, will be explained.

FIG. 5 is a flow chart for explaining the procedure of manufacturingvarious microdevices, such as semiconductor chips (e.g., ICs or LSIs),liquid crystal panels, CCDs, thin film magnetic heads or micro-machines,for example. Step 1 is a design process for designing a circuit of asemiconductor device. Step 2 is a process for making a mask on the basisof the circuit pattern design. Step 3 is a process for preparing a waferby using a material such as silicon. Step 4 is a wafer process, which iscalled a pre-process, wherein, by using the thus prepared mask andwafer, a circuit is formed on the wafer in practice, in accordance withlithography. Step 5, subsequent to this, is an assembling step, which iscalled a post-process, wherein the wafer having been processed at step 4is formed into semiconductor chips. This step includes an assembling(dicing and bonding) process and a packaging (chip sealing) process.Step 6 is an inspection step wherein an operation check, a durabilitycheck, and so on, for the semiconductor devices produced by step 5, arecarried out. With these processes, semiconductor devices are produced,and they are shipped (step 7).

FIG. 6 is a flow chart for explaining details of the wafer process. Step11 is an oxidation process for oxidizing the surface of a wafer. Step 12is a CVD process for forming an insulating film on the wafer surface.Step 13 is an electrode forming process for forming electrodes upon thewafer by vapor deposition. Step 14 is an ion implanting process forimplanting ions to the wafer. Step 15 is a resist process for applying aresist (photosensitive material) to the wafer. Step 16 is an exposureprocess for printing, by exposure, the circuit pattern of the mask onthe wafer through the exposure apparatus described above. Step 17 is adeveloping process for developing the exposed wafer. Step 18 is anetching process for removing portions other than the developed resistimage. Step 19 is a resist separation process for separating the resistmaterial remaining on the wafer after being subjected to the etchingprocess. By repeating these processes, circuit patterns are superposedlyformed on the wafer.

With these processes, high density microdevices can be manufactured withdecreased cost.

While the invention has been described, with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.2003-388129 filed Nov. 18, 2003, which is hereby incorporated byreference.

1. A holding system, provided on a movable stage, for holding an objectfrom above, against gravity, said holding system comprising: at leastone holding portion adapted to be in contact with the object, to holdthe object from the above; and at least one attracting portion forattracting a limited portion of the object upwardly, without contactthereto.
 2. A holding system according to claim 1, wherein said holdingportion is adapted to hold the object on the basis of one ofelectrostatic force, vacuum attraction, electromagnetic force andmechanical holding.
 3. A holding system according to claim 1, whereinsaid attracting portion attracts the limited portion of the object onthe basis of electrostatic force.
 4. (canceled)
 5. (canceled)
 6. Aholding system according to claim 1, wherein said holding systemincludes three of said holding portions.
 7. A holding system accordingto claim 1, wherein at least one of said holding portion and saidattracting portion includes a flowpassage along which a temperatureadjusted medium can pass.
 8. (canceled)
 9. A holding system according toclaim 1, further comprising a mirror, wherein said holding system holdsthe mirror.
 10. A holding system according to claim 1, wherein theoriginal is a reflection type original and wherein said holding systemholds the reflection type original.
 11. A holding system according toclaim 1, wherein said holding system holds the substrate.
 12. A holdingsystem according to claim 10, wherein the holding portion holds a bottomsurface portion of the reflection type original, while avoiding a regionthereon corresponding to a pattern region.
 13. A holding systemaccording to claim 10, further comprising a base plate for holding atleast one of the holding portion and the attracting portion, said baseplate being held by an original stage.
 14. A holding system according to8 claim 1, further comprising a surface measuring unit for measuring ashape of a bottom surface of the object held by said holding system,wherein the attraction force of said attracting portion is controlled inaccordance with the measurement made by said surface measuring unit. 15.A holding system according to claim 1, wherein at least one of saidholding portion and said attracting portion includes a flowpassage alongwhich a temperature adjusted medium can pass.
 16. A holding systemaccording to claim 13, wherein said base plate includes a flowpassagealong which a temperature adjusted medium can pass.
 17. (canceled)